The present invention generally relates to an intelligent electronic device, and more specifically, to an apparatus and method for compensating digital input delays and communication delays in and between an intelligent electronic device.
Electric power systems are designed to generate, transmit and distribute electrical energy to loads. In order to accomplish this, power systems generally include a variety of power system elements such as electrical generators, electrical motors, power transformers, power transmission lines, buses and capacitors, to name a few. As a result, power systems typically include intelligent electronic devices (IEDs) in communication with power system elements for protection, monitoring, controlling, metering or automation of at least a portion of the power system. For example, an IED may communicate with a power system element in order to protect a portion of the power system from abnormal conditions such as electrical short circuits, overloads, frequency excursions, voltage fluctuations, and the like. IEDs used in an electric power system may generally include protective relays or otherwise, remote terminal units (RTUs), power line communication devices (PLCs), bay controllers, supervisory control and data acquisition (SCADA) systems, general computer systems, meters, and any other comparable devices used for protecting, monitoring, controlling, metering and/or automating a portion of the electric power system.
In some cases, IEDs may include a recording function generally referred to as a sequential event recorder (SER) adapted to record and time-stamp a variety of events associated with an associated power system element. A SER may be adapted to provide a report which generally includes the date, time, power system element name or type, and an event associated with the power system element (e.g., the state of the power system element). Some IEDs are referred to as SERs, wherein their dedicated function is to record and time-stamp a variety of events associated with an associated power system element.
For example, one typical IED including a SER is a protective relay having a SER that provides information on what are generally known in the art as relay word bit states and relay element operations. Relay word bits are generally known in the art to refer to binary states such as relay protection logic inputs or outputs, the general operation of the power system element, or the power up or shutdown sequences of the power system element. Relay element operations are generally known in the art to include operations such as relay power up, relay enable and disable, settings changes, and SER automatic removal and reinsertion. A SER may also record state changes. For example, a SER may record state changes via user specified relay word bits listed in what are known as SER trigger equations.
In general, traditional SERs used in conventional power system IEDs are deficient in that they have a general inability to compensate for time delays in communication of the data signal between the IED and the power system element or among various elements within the IED. As a result, the reports provided by a SER of an IED may be generally incorrect due to the lack of compensation for such time delays. For example, the IED may provide a report containing time-stamped events which are listed in a generally incorrect chronological order causing for difficult analysis.
Accordingly, it is an object of the present invention to provide an apparatus and method for compensating for time delays in communication of the data signal between the IED and the power system element or among various elements within the IED. It is further an aspect of the present invention to provide an apparatus or method for providing a SER report containing time-stamped events which are listed in a generally correct chronological order.
Some conventional IEDs comprising a SER are further deficient in that they are generally unable to detect accidental state changes in the power system element. For example, a power system element may be adapted to include a mechanical contact which is actuated upon the changing of the status of the power system element. The mechanical contact may have an electrical contact which is actuated a plurality of times during an initial mechanical contact. The plurality of actuations of the electrical contact may cause a ripple or bouncing in the resulting data signal which is communicated from the power system element to the IED. Conventional IEDs having a SER are generally deficient in that they are unable to accurately discern between a valid data signal and an accidental data signal. Conventional IEDs are further deficient in that they are generally unable to compensate for the time delay due to such bouncing or ripple in the data signal. As such, conventional IEDs having a SER often record an accidental data signal erroneously as a valid data signal.
Accordingly, it is an object of the present invention to provide an apparatus and method for accurately discerning between a valid data signal and an accidental data signal while also accurately associating a time with the data related thereto using a novel edge detection element. It is further an object of the present invention to provide an apparatus and method for compensating for the time delay due to such bouncing or ripple in the data signal. A present invention method is also provided which facilitates the reduction of processing burden of the IED and optimization of system performance.
These and other desired benefits of the preferred embodiments, including combinations of features thereof, of the invention will become apparent from the following description. It will be understood, however, that a process or arrangement could still appropriate the claimed invention without accomplishing each and every one of these desired benefits, including those gleaned from the following description. The appended claims, not these desired benefits, define the subject matter of the invention. Any and all benefits are derived from the multiple embodiments of the invention, not necessarily the invention in general.